Conventionally, using the coupling between pins fixed to lens frames (a moving frame) of lenses and cam grooves formed in a plurality of cylindrical members telescopically fit, the lenses are driven in the optical axis direction.
However, in such a cam mechanism, even if it is intended to make smaller the cylindrical members with the cam grooves formed on them and the parts such as pins engaged to them, there are limitations on processing and assembling, thus a problem arises that the miniaturization of the cam mechanism cannot follow the miniaturization of the optical system.
Further, in the cam mechanism aforementioned, there is installed an inclination control mechanism for preventing each lens moving back and forth in the optical axis direction from being inclined to the optical axis, however, it is difficult to prevent inclination of the lenses because the moving frame for holding the lenses moves back and forth while rotating around the optical axis, and the span of the inclination control mechanism cannot be long enough when intending to miniaturize a plurality of moving frames by avoiding the mutual interference.
Therefore, a cylindrical drive shaft having a spiral thread on the outer peripheral surface thereof is arranged in parallel with the optical axis of the lenses, and a thread coupled to the thread of the drive shaft is formed on the lens frame, and the lenses are moved in the optical axis direction by the rotation of the drive shaft. In this case, it is necessary to prevent inclination of the optical axis and displacement thereof and for that purpose, and it is general to install a guide shaft in parallel with the optical axis of the lenses and to form a through hole passing through the guide shaft in the lens frame so as to support movably the lens frame by the guide shaft. By use of this constitution, the lens barrel is not restricted on its shape, and a drive section for rotating the drive shaft can be arranged in the lens barrel together with the drive shaft and guide shaft, thus the size as a whole can be controlled easily.
In recent years, by use of, adding to such a constitution, a bending optical system for bending the optical axis of the imaging optical system by a mirror or a prism, thinning of a camera (miniaturization in a depth direction) has been realized (for example, refer to Japanese Laid-Open Patent Publication 2005-352236).
Further, a method for driving a moving lens in the optical axis direction using a linear drive mechanism using an electro mechanical element such as a piezo element is also employed. (For example, refer to U.S. Pat. No. 6,134,057.)
However, in the lens drive mechanism disclosed in U.S. Pat. No. 6,134,057, the lens frames for holding two lens groups are driven independently to optional positions by the linear drive mechanism, so that particularly when zooming, it is necessary to detect the position of each lens frame with high precision. Therefore, a sensor for detecting a highly precise position and a signal processor are necessary, which causes obstacles to miniaturization. To solve such a problem, a method for interlocking and driving two lenses by a plate cam mechanism is disclosed (for example, refer to U.S. Pat. No. 6,618,212) focusing attention on the relationship that is uniquely decided between the imaging magnification and the positional relationship between the two lens groups.
However, in the constitution of U.S. Pat. No. 6,618,212, the two lens groups are driven by the plate cam mechanism, and a cam in a size corresponding to the moving distance of the lenses is necessary, thus the cam mechanism becomes larger, which causes obstacles to realization of miniaturization and lightweight.